Avoid zooming in when zooming out over certain areas of chart (#574)

* Avoid zooming in when zooming out over certain areas of chart

Zooming out when hovering over y-axis labels or legend would cause `minPercent` to be negative or past 100%, causing the chart to zoom in instead.

* Update src/scale.types.js

Co-authored-by: Jukka Kurkela <jukka.kurkela@gmail.com>

src/scale.types.js

@@ -6,7 +6,12 @@ function zoomDelta(scale, zoom, center) {
   const newRange = range * (zoom - 1);
 
   const centerPoint = scale.isHorizontal() ? center.x : center.y;
-  const minPercent = (scale.getValueForPixel(centerPoint) - scale.min) / range || 0;
+  // `scale.getValueForPixel()` can return a value less than the `scale.min` or
+  // greater than `scale.max` when `centerPoint` is outside chartArea.
+  const minPercent = Math.max(0, Math.min(1,
+    (scale.getValueForPixel(centerPoint) - scale.min) / range || 0
+  ));
+
   const maxPercent = 1 - minPercent;
 
   return {